Session Initiation Protocol (SIP) is one of multimedia communications system framework protocols established by Internet Engineering Task Force (IETF). SIP is a text based application layer control protocol and is independent of bottom layer protocol. SIP is used for setting up, modifying, and terminating two-party or multi-party multimedia sessions over Internet Protocol (IP) networks. In networks using SIP (e.g., IMS networks) a forking transmission method which allows a SIP message to be received by a plurality of user terminals associated with a user identifier is provided.
The forking transmission for SIP networks includes the following steps described below. Correspondence is set up between a user identifier and information of a plurality of user terminals (e.g., correspondence between a user identifier and addresses of a plurality of user terminals) in a proxy at the SIP network side. When a SIP message for the plurality of user terminals is received at the SIP network side, the SIP message is firstly forwarded to the proxy and based on the pre-set correspondence, the proxy finds out the information of the plurality of user terminals which correspond to the user identifier in the SIP message. Then the SIP message is forwarded to the plurality of user terminals corresponding to the information of the plurality of user terminals.
At present, forking transmission in SIP networks may be performed in two ways: parallel forking transmission and sequential forking transmission. In parallel forking transmission, a proxy sends several copies of a SIP message to a plurality of user terminals. While in sequential forking transmission, a proxy sends a received SIP message to a first user terminal according to a sequence pre-set for the plurality of user terminals corresponding to a same user identifier and stops sending the SIP message to other user terminals if a transmission success response is received from the first user terminal. Otherwise the proxy continues sending the SIP message to other user terminals in the pre-set sequence until a transmission success response is received or the SIP message has been sent to all the user terminals.
IMS networks are based on the SIP technology in which multimedia services are established, managed, and terminated by using a SIP call control scheme. SIP forking transmission can be adopted in an IMS network in which a proxy may be implemented by a Service-Call Session Control Function (S-CSCF) at the IMS network side. When the S-CSCF receives registration information of a user terminal, a public user identifier being used by the user terminal will be associated with the address of the user terminal and then saved. If a public user identifier is associated with addresses of a plurality of user terminals, forking transmission will take place at the S-CSCF in transmitting a SIP message to the public user identifier. The forking transmission performed by the S-CSCF is pre-configured to be parallel or sequential for sending the received SIP message. In other words, when a plurality of user terminals are associated with a same public user identifier, the user corresponding to the public user identifier may set the incoming SIP messages to be sent in parallel forking or sequential forking by configuring user data at the S-CSCF.
The SMS is fully developed and widely applied in the conventional Circuit Switched (CS) domain. In an effort to continuously develop SMS such that SMS may be experienced by users in future IP networks, 3GPP (Third Generation Partnership Project) has established a research initiative directed towards SMS over IP. According to one method provided by the research, an IP-Short-Message-Gateway (IP-SM-GW) is set up in an IP network as an SMS gateway between an IMS network domain and a CS domain. When an SMS message is sent from the IMS network domain to the CS domain, the SMS message is encapsulated into a SIP message body and sent to the IP-SM-GW. The IP-SM-GW parses the received SIP message body to retrieve the SMS message and sends the SMS message to the CS domain. When an SMS message is sent from the CS domain to the IMS network domain and received by the IP-SM-GW, the IP-SM-GW constructs a SIP message in whose message body the SMS message is encapsulated and sends the SIP message to the IMS network domain. According to another method for transmitting SMS messages over an IP network, an IP-SM-GW is set up in the IP network as a message gateway between the IMS network domain and the CS domain. When an SMS message is sent from the IMS network domain to the CS domain, the content of the SMS message is extracted, loaded into a SIP message body, and sent to the IP-SM-GW. The IP-SM-GW parses the received SIP message body to retrieve the content of the SMS message, constructs an SMS message, and sends the SMS message to the CS domain. When an SMS message is sent from the CS domain to the IMS network domain and received by the IP-SM-GW, the IP-SM-GW constructs a SIP message whose message body carries the content of the SMS and sends the SIP message to the IMS network domain.
However, both ways of sending SMS messages between the CS domain and the IMS network domain have a defect: it is impossible to manage an SMS message from the CS domain to be delivered in the IMS network domain to more than one user terminal in a forking manner.